Polyester-carbonates are known thermoplastic resins whose many excellent physical properties allow them to be used successfully in many commercial and industrial applications. This is especially true of aromatic polyester-carbonates. However, in some applications a material having a higher heat distortion temperature, higher flexural strength and greater tensile strength than aromatic polyester-carbonate resin is required.
The addition of various additives in attempting to provide an aromatic polyester-carbonate resin which has a higher heat distortion temperature, higher flexural strength and greater tensile strength have produced mixed results. In some instances there was no improvement in the heat distortion temperature, flexural strength, or the tensile strength of the polymer. In other instances the addition of certain additives to the aromatic polyester-carbonate resulted in a polymer having a higher heat distortion temperature, higher flexural strength and greater tensile strength, but this was accomplished only at the expense of some of the other valuable properties of the polyester-carbonate.
This is due to the fact, well known to those skilled in the art, that the area of modification of the physical properties of a polymer by the addition of various additives thereto is largely an empirical art rather than a predictable science with little, if any, predictability on the effects a particular additive will have in a particular polymer.
Thus, while a particular additive may have one effect in one polymer system the same additive may well produce entirely different results when used in another and different polymer system. Likewise, two rather closely related additives may produce entirely different results when added to the same polymer system.
There thus exists a need for an aromatic polyester-carbonate resin which has a higher heat distortion temperature, greater tensile and flexural strength, and yet retains all of the advantageous physical properties of an unmodified aromatic polyester-carbonate.